A large number of persons commonly suffer from hemiparesis or hemiplegia. Persons with hemiparesis suffer from weakness on one side of the body. That is, the patient can move an arm, leg, and/or trunk associated with an impaired side of their body, but with reduced muscular strength. Persons with hemiplegia are afflicted with paralysis of the arm, leg, and/or trunk on the same side of the body. Hemiplegia and hemiparesis may be congenital, or they might be acquired conditions resulting from an illness, an injury, or a stroke.
Whether a person is suffering from hemiparesis or hemiplegia, the end result is extreme difficulty performing everyday tasks. In particular, many activities of daily living entail bimanual tasks, which either require or are greatly facilitated by the use of two hands. In many bimanual tasks, one arm and hand are used essentially to provide support or resistance, while the other arm and hand are used to provide power or movement. Examples include twisting a lid off of a jar, slicing a loaf of broad, turning the page of a book, taking currency out of a wallet, etc. Still other tasks use one or both arms to hold an object, but do not otherwise require motive power. Examples include holding a bag or briefcase (single-arm holding tasks), or holding a laundry basket (bimanual holding task).